Anesthesiology

Muscle flap coverage of sternal wound infections – Procedures

What the Anesthesiologist Should Know before the Operative Procedure

Surgical site infections are second only to urinary tract infections as a cause of nosocomial infections. Such infections are divided into superficial sternal site infections (SSSIs) and deep sternal site infections (DSSIs). DSSIs are a major source of morbidity, mortality, and cost for patients having undergone cardiac surgery. The incidence may range from 0.5% to 5% after sternotomy with a mortality rate of 5% to as high as 50% depending upon the organism. Such infections may triple the cost of care due to a longer length of hospital stay, longer ICU stay, and increased likelihood of readmission to an ICU. Although DSWIs are associated with early mortality after discharge, long-term mortality is no different than those patients that undergo cardiac surgery but do not develop an infection.

Many risk factors have been cited. Patient-specific factors include female sex, use of steroids, current smoking, hypertension, older age, obesity, poor functional status, diabetes, postoperative hyperglycemia, low cardiac output and ejection fraction, and preoperative addiction to opiates. Surgery-specific risk factors include excessive bleeding after the initial procedure, reoperation, longer duration of surgery, surgery performed on intra-aortic balloon counter pulsation, and retention of drainage catheters in the surgical site for more than 48 hours. Early tracheostomy does not appear to be a risk factor for mediastinitis. The risk associated with bilateral internal mammary artery harvest is controversial. The most common organisms are coagulase-negative Staphylococcus epidermidis and Staphlococcus aureus. Methicillin-resistant Staphlococcus aureus (MRSA) is assuming a more important role and has a higher incidence of death.

An SSSI involves only the skin and subcutaneous tissue of the incision with either purulent drainage, microorganisms, or pain, redness, and swelling. A DSSI involves the fascial and muscle layers or organ spaces and pus in the deep incision, spontaneous dehiscence of the wound, an abscess diagnosed by computed tomography, or a diagnosis of osteomyelitis or mediastinitis.

The anesthesiologist’s role in the management of surgical site infections begins at the time of the initial procedure with adherence to specific practice that has been proved to decrease the incidence of infection. Such practice includes maintenance of normothermia, avoidance of hyperglycemia, avoidance of unnecessary blood product transfusions, and timely, appropriate antibiotic prophylaxis.

Certain aspects of cardiac surgery may predispose patients to infections. Cardiopulmonary bypass compromises the immune system through reduced phagocytosis, activation of white blood cells, and impaired humoral immunity. Induced hypothermia and the duration of the procedures further increase the risk of infection as does postoperative bleeding. Patients commonly have many drains in place after surgery providing a conduit from the surface to deeper structures.

The Society of Thoracic Surgeons (STS) have made recommendations and published guidelines that attempt to standardize practice with a goal of decreasing wound infections and reducing the development of resistant organisms (Table I).

1. What is the urgency of the surgery?

Certain practices to prevent wound infections should be standard regardless of the urgency of the surgery. This includes adherence to sterile technique, timely selection and administration of appropriate antibiotics. Adherence to sterile technique during central line placement includes mask, gown, sterile gloves, and full body draping during line placement. Central line protocols may dictate that lines placed under emergent conditions when violation of sterile technique occurs be changed after the procedure if maintenance of sterile technique is not guaranteed.

What is the risk of delay in order to obtain additional preoperative information?

DSSIs are associated with significant mortality in the first 30 days after cardiac surgery. It does appear that long-term mortality is higher even in patients treated appropriately. Thus urgent surgical management is imperative to reduce long-term mortality. The risk associated with delay in management includes the development of systemic involvement and infection of prosthetic material including grafts, artificial valves, or implanted devices.

The presence of DSSI associated with mediastinitis is a medical emergency requiring immediate surgical drainage. Patients may demonstrate manifestations of sepsis including hypotension, ARDS, renal or hepatic dysfunction, and septic myocardial depression.

2. Preoperative evaluation

The preoperative evaluation will generally start with an effort to determine whether the infection is a superficial sternal site infection (SSSI) or a deep sternal site infection (DSSI). The anesthesiologist should review records related to the initial surgical procedure including airway management, intravenous access, and intraoperative course. Patients that present for cardiac surgery have a higher rate of difficult laryngoscopy than patients presenting for non-cardiac surgery.

3. What are the implications of co-existing disease on perioperative care?

Coexisting diseases may affect the incidence of disease and survival after diagnosis including the risk of death after treatment with muscle flap advancement.

a. Cardiovascular system

Patients with impaired left ventricular function and/or advanced heart failure as defined by class III or IV New York Heart Association heart failure are at higher risk for DSSI. These conditions may be improved after the initial cardiac surgery (CABG, valve repair or replacement) but not necessarily. Some conditions may be worse. The systemic effects of infection may worsen ventricular function. Arrhythmias are also more common in patients with DSSI. Patients with systemic manifestation of infection may have associated endocarditis. Transthoracic echocardiography (TTE) or transesophageal echocardiography (TEE) may allow accurate diagnosis.

b. Pulmonary

Coronary artery bypass grafting (CABG) via a sternotomy induces many changes in pulmonary function that persist for weeks and months. Forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), and peak expiratory flow rate (PEFR) are compromised for at least 3 months. This is likely due to capillary leak, edema, and atelectasis. Sternal pain or sternal non-union may impair ventilation in the immediate postoperative period. Chronic obstructive pulmonary disease (COPD) has been identified in some studies as a risk factor for DSSI. Baseline oxygen saturation and arterial blood gas analysis may help predict the likelihood of successful extubation. Some sternal infections are so severe as to warrant full sternal removal and flap closure only. Such a procedure may have a significant impact on respiratory mechanics.

c. Renal-GI:

Postoperative renal failure is identified as a risk factor for DSSI. Such patients may demonstrate heart failure and pulmonary edema in addition to difficulty with fluid management. Antibiotics should be dosed appropriately based upon renal function.

d. Neurologic:

Neurologic status has not been identified as a risk factor for DSSI although agitation after surgery can increase the risk of sternal instability and infection. Manifestations of infection in the elderly population are often nonspecific. Confusion and delirium may be the only indication of a deep infection.

f. Endocrine:

Patients with diabetes are at an increased risk for sternal site infections as are patients without diabetes but who exhibit hyperglycemia in the perioperative period. Both morbidity and mortality are reduced when hyperglycemia is controlled. Control of hyperglycemia and maintenance of glucose levels to less than 200 mg/dL have resulted in a reduction in the incidence of such infections. The Society of Thoracic Surgeons has published guidelines for the perioperative management of hyperglycemia. These guidelines target a glucose level less than 180 mg/dL.

4. What are the patient's medications and how should they be managed in the perioperative period?

Patients with DSSI are often treated with antibiotics prior to the surgical procedure. Such antibiotics must be continued into the perioperative period. Anticoagulants such as Coumadin and antiplatelet agents create a baseline coagulopathy, which may translate into increased perioperative bleeding. Also, patients having undergone cardiac surgery will be managed with beta-blockers and cholesterol-lowering agents as these are quality measures by many organizations. Beta-blockers should be continued into the perioperative period unless there is evidence of acute heart failure.

h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

Anticoagulants such as Coumadin and antiplatelet agents create a baseline coagulopathy, which may translate into increased bleeding during the perioperative period, especially in patients subject to repeat sternotomy. Plavix (clopidogrel) should generally be discontinued 7 days before elective procedures but may place a patient with a coronary stent at risk for thrombosis. The decision as to when to discontinue antiplatelet agents in a patient with a stent should be made in conjunction with the cardiologist and surgeon. Risk is highest in those patients with drug eluting stents

i. What should be recommended with regard to continuation of medications taken chronically?

Cardiac:

Quality indicators for patients having undergone CABG include the prescription of a beta-blocker, aspirin, and cholesterol-lowering agent upon discharge from the hospital. Beta-blockers and cholesterol-lowering agents should be continued into the perioperative period. Angiotensin-converting enzyme inhibitors should be discontinued 24 hours prior to surgery if possible. Patients with coronary stents receiving antiplatelet therapy are at high risk for thrombosis should antiplatelet agents be discontinued in the perioperative period. Surgery for superficial and deep surgical site infections cannot be delayed. A multidisciplinary approach involving the cardiologist and surgeon is necessary for determining a safe plan and to monitor for complications.

Pulmonary:

Bronchodilators should be continued.

j. How To modify care for patients with known allergies –

A rare but challenging situation arises when a patient with a known IgA deficiency presents for redo cardiac surgery. A small percentage of such patients will exhibit anaphylaxis to blood transfusion. The blood bank must be notified as soon as possible to make arrangements. Blood cells should be washed. Fresh frozen plasma and platelets must come from patients with known IgA deficiency through an established donor network. Surgery for a DSSI may not allow time to obtain platelets and FFP. A discussion with the blood bank and surgeon must occur ahead of time and plans made for treating bleeding and coagulopathy.

Allergic reaction to natural latex rubber can result in life-threatening anaphylaxis with exposure to products in the operating room containing natural-rubber latex. The prevalence of IgE antibodies to latex may be as high as nearly 7% in the general population. Patients with myelodysplastic syndromes and urogenital abnormalities are at higher risk as are patients with a history of fruit allergy including banana, avocado, and kiwi. A complete preoperative anesthesia evaluation should reveal any risk of a history of reaction. The history should include reactions to latex gloves. Reactions range from simple rash to full anaphylaxis. Sources of latex in the operating room include gloves, stoppers in medication vials, rubber tourniquets, surgical drains, and urinary catheters.

All operating room personnel should be aware of a patient with a latex allergy. Latex gloves should be removed from the room or isolated to avoid inadvertent use and a non-latex alternative made available. All medications should be prepared without puncturing latex stoppers although this has not been shown to reduce latex levels. Premedication with histamine blocking agents has been recommended although this does not necessarily prevent a reaction.

Medications and a plan for resuscitation should be made ahead of time. Epinephrine, steroids, and antihistamines should be readily available.

Most central lines and introducers are now latex free. The balloon on a flow-directed pulmonary artery catheter contains natural latex rubber. Latex-free pulmonary artery catheters are available but at higher expense.

l. Does the patient have any antibiotic allergies

Cephalosporins are the drug of choice for the prophylaxis of surgical site infections. Patients with a sensitivity to cephalosporins should receive vancomycin and additional coverage for gram-negative organisms, either gentamicin or levofloxacin.

m. Does the patient have a history of allergy to anesthesia?

Malignant hyperthermia (MH) is an autosomal dominant condition that manifests as a hypermetabolic state when an individual is exposed to a triggering agent. Agents that may trigger the reaction include volatile anesthetics (halothane, isoflurane, enflurane, sevoflurane, and desflurane) and succinylcholine. Even trace amounts of the agents can trigger such a reaction.The syndrome will manifest as overproduction of carbon dioxide, muscle rigidity, metabolic and respiratory acidosis, and hemodynamic collapse.

A complete preoperative evaluation should include questions about a history of MH or abnormal reactions to anesthesia in the patient or family members. The absence of such a history does not rule out the possibility of MH but makes it unlikely.

The operating room should be prepared. All triggering agents should be removed (volatile agents and succinylcholine). All vaporizers should be removed from the anesthesia machine. The CO2 absorber should be replaced. Reservoir bags and tubing should be changed as rubber may absorb volatile agents. The machine should be flushed for 5 minutes at least with 10L flow of oxygen prior to use.

The clinical symptoms of MH include tachycardia, tachypnea, arrhythmias, unstable blood pressure, sweating, rigidity, and dark blood on the surgical field. Surgery should be stopped as soon as possible should MH be suspected. Help should be summoned and 100% oxygen should be administered immediately.

The treatment for suspected MH is dantroline, a lyophilized formulation containing mannitol and sodium hydroxide. Dantroline must be dissolved in sterile water and is administered in a dose of 2.5 mg/kg, repeated up to a total of 10 mg/kg. Additional support includes administration of sodium bicarbonate to treat acidosis and hyperkalemia, maintenance of urine output, and intense monitoring. An arterial line should be placed. Intensive care is indicated after the diagnosis.

5. What laboratory tests should be obtained and has everything been reviewed?

Patients with sternal wound infections often present within the first 30 days after the initial surgery. Common laboratory abnormalities include anemia, elevated prothrombin time if the patient is taking coumadin, leukocytosis with a left shift, and an increase in blood urea nitrogen (BUN) and serum creatinine. Blood antibody sampling is imperative and may demonstrate development of abnormal antibodies.

Hemoglobin levels:

Anemia is associated with the initial surgical procedure and current infection. The administration of blood products may also increase the risk of infection.

Electrolytes:

Hypokalemia and hypomagnesemia may predispose the vulnerable patient to arrhythmias. Hyponatremia may be seen in patients on thiazide diuretics.

Coagulation panel:

Patients are often anticoagulated with coumadin after surgery due to mechanical prosthesis or atrial fibrillation.

Electrocardiogram:

Arrhythmias are common in patients with DSSI.

Imaging:

Computed chest tomography may reveal several indicators of DSSI including sternal non-union and abscess formation. Abscess formation may be especially critical in patients with prosthesis such as valves or aortic grafts. Aortic graft disruption has been reported in the presence of DSSI.

Other tests:

TTE or TEE may reveal the presence of vegetations indicating endocarditis or additional cardiac involvement. Blood cultures may reveal bacteremia.

6. Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

Some very minor SSSIs may be managed with monitored anesthetic care during the initial exploration and drainage. Often it is difficult to determine the degree of tissue involvement and viability by preoperative studies and exploration is necessary. All DSSIs will require general anesthesia.

a. Regional anesthesia

Neuraxial anesthesia has been employed successfully in the management of patients undergoing CABG. The benefits may include improved cough, better pain control, and less nausea and vomiting but the literature is unclear regarding benefit. Patients undergoing redo sternotomy for DSSI are by definition infected. Bacteremia may induce epidural abscess formation in the presence of neuraxial anesthesia.

b. General Anesthesia

General anesthesia is selected for all DSSIs. General anesthesia allows for deep wound exploration and full debridement including placement of vacuum assisted drainage and omental transfer. Muscle flap advancement often requires muscle relaxation and only general anesthesia will suffice. General anesthesia does require endotracheal intubation. Patients with COPD are at risk for sternal wound infection. Such patients are often difficult to extubate due to the change in pulmonary mechanics associated with sternal debridement and in some cases full sternal removal.

Patients presenting for cardiac surgery have a higher incidence of difficult laryngoscopy than patients presenting for other procedures. This may be due to diabetes and “diabetic stiff joint syndrome” or poor neck mobility often seen in elderly patients. By definition, DSSIs have occurred after a prior sternotomy; thus airway records are available and should be reviewed prior to the procedure.

c. Monitored Anesthesia Care

Monitored anesthesia care (MAC) may be successful for drainage of small superficial skin infections and avoids the morbidity associated with intubation. MAC may also be associated with less morbidity in patients who require multiple dressing changes and minor debridements after the initial deeper surgical exploration. MAC would not be adequate during the initial deep sternal debridement and later muscle flap placement. A single agent or combination of agents that provides both analgesia and sedation should be selected. A benzodiazepine such as midazolam and opioid such as fentanyl are easy to titrate. Ketamine in small doses will provide intense analgesia without respiratory depression. Ketamine should be administered with a benzodiazepine to avoid unpleasant hallucinations. MAC does require the same level of basic monitoring as a general anesthetic for the same duration of time.

7. What is the author's preferred method of anesthesia technique and why?

What prophylactic antibiotics should be administered?

Antibiotics administered in the perioperative period during debridement of a DSSI should be tailored to treat the specific infecting organism if possible. The most common infecting organisms are Staphylococcus epidermidis and Staphylococcus aureus. Broad-spectrum antibiotics are indicated in the case of toxemia. Should an organism not be identified, routine prophylaxis with a cephalosporin is indicated.

What do I need to know about the surgical technique to optimize my anesthetic care?

The preoperative evaluation will include a computed tomography of the chest to determine the depth of tissue involvement and whether an abscess has formed. It is wise to plan for a major debridement. Most DSSIs will present in the first 30 days. This is the period of time where thoracic reoperation is most risky due to the presence of very dense, vascular adhesions below the sternum. Structures such as the right ventricle, right atrium, coronary grafts, pulmonary artery, or cardiac patches may be adherent to the sternum. Redo sternotomy and dissection may risk injury and massive hemorrhage. Patients presenting for deep sternal exploration are managed as is any repeat sternotomy case, with arterial line placement and large IV access. SSSIs are managed with debridement and closure by secondary intention, often with vacuum-assisted closure (VAC) dressings. DSSI are managed with deep debridement. Such procedures may involve debridement of sternal bone until viable tissue is noted. Extensive sternal debridement may be required. Sometimes sternal debridement, mediastinal irrigation, and sternal re-wiring are used alone. Most closures are delayed while the patient is treated with vacuum drainage and antibiotics. Definitive closure occurs days to weeks after the initial debridement. Most patients will undergo sternal closure with sternal rewiring or muscular advancement/rotational flaps with either a unilateral or bilateral pectoralis major. The rectus abdominis may also be used.

What are the most common intraoperative complications and how can they be avoided/treated?

Prioritize them by urgency. The anesthesiologist must be prepared for the most catastrophic complication of redo sternotomy and debridement of mediastinitis: damage to underlying structures and massive hemorrhage. Large peripheral and/or central venous access is indicated. Blood products should be ordered and readily available. Our practice is to place all intravenous access on the right side in the case of damage to the left brachiocephalic vein during chest opening. Arterial pressure monitoring should occur on the right side as well. TEE may be beneficial to evaluate for endocarditis and extension of infection. Hypothermia should be avoided by maintaining a warm room, warming all fluids, and using a warming blanket.

What are risk factors for mortality after muscle flap advancement and why?

Deep sternal wound infections are associated with significant mortality. Factors associated with increased mortality after muscle flap advancement include presternotomy end-stage renal disease, presternotomy COPD, and prolonged poststernotomy mechanical ventilation. Patients with end-stage renal disease are immunosuppressed. End-stage renal disease patients often lack the ability to readily deal with fluid shifts. Patients with COPD who are treated with steroids are at risk for impaired wound and sternal healing. Prolonged mechanical ventilation may result in continual contamination of the sternal wound. Other factors potentially associated with a higher mortality rate include increased body weight and female sex.

a. Neurologic:

N/A

b. If the patient is intubated, are there any special criteria for extubation?

Most patients who have undergone debridement for DSSI will be extubated in the operating room. Patients with COPD benefit from early extubation but sternal instability or opening may interfere with effective respiratory mechanics. Adequate pain control is imperative.

c. Postoperative management

What analgesic modalities can I implement?

Excessive pain after sternal debridement is rare. Most patients can be adequately managed with oral opioids such as oxycodone. Others may be more effectively managed with patient controlled analgesia. Neuraxial anesthesia (epidural) is rarely necessary and may be contraindicated due to fears of epidural abscess formation in the setting of infection.

What level bed acuity is appropriate?

Patients having undergone debridement for SSSI are unlikely to be unstable or require prolonged extubation. Routine postanesthesia monitoring followed by floor management is appropriate. Patients having undergone initial debridement for DSSI are best managed in an intensive care unit setting.

Are there any other considerations for patients with VAC dressings after surgery?

VAC dressing placement or negative pressure wound therapy (NPWT) may be associated with major complications. Although rare, right ventricular rupture, bleeding from vein grafts, and bleeding from an aortic homograft have been reported and associated with significant mortality. This may bve due to disruption of the heart during therapy. VAC bleeding of the heart can be reduced by application of a non-adherent layer between the heart and VAC sponge.

Are there any other potential treatments?

Hyperbaric oxygen (HBO) has been utilized successfully to augment management of refractory necrotizing soft tissue infection and sternal osteomyelitis. Utilization of HBO is labor intensive, often requires significant patient transport, time, as well as multiple treatment cycles. There may be benefit in a limited number of patients.

Mauermann, WJ, Nemergut, EC. “The anesthesiologist's role in the prevention of surgical site infections”. Anesthesiology. vol. 105. 2006. pp. 413-21. (This article review 6 perioperative factors over which an anesthesiologist may affect the development of infection in the perioperative period.)